1. Field of the Invention
This invention relates to a method for making a cable splice joining the broken end portions of a flexible electrical cable and more particularly a method for splicing together the broken end portions of a flexible cable that includes a formed metallic sleeve arranged to frictionally engage the joined cable end portions and permit optimum flexing of the cable without destroying the cable splice.
2. Description of the Prior Art
In underground mining substantially all of the equipment is electrically driven and the power is supplied by means of conductor cables. The conductor cables extend for substantially long distances and when connected to movable mining equipment are subjected to abrasion, moisture and frequent flexing, as for example, when the cable is wound on a cable reel and when the cable extends around pulleys mounted on the mining equipment. Adverse conditions to which the cable is subjected frequently result in a parting of the conductors and it is necessary to either splice or replace the cable before mining operations can resume. A splice, therefore, should be made with a minimum of tools at the location of the break in the cable and by one having ordinary skills with the tools.
When the broken cable is spliced in the field such as in a mine haulageway, the cable must meet minimum conditions in that it be moisture-resistant and retain flexibility to be wound on the cable reel without parting the splice. It is highly desirable to provide a splice that will part when the cable is subjected to a tensile strength up to but not in excess of the maximum safe tensile strength of the cable. The cable can then be respliced at the previous splice in a shorter period of time than is required to prepare a new splice. There are also regulations that limit the number of splices that can be made in the cable used in underground mining.
Conventional compression-type couplings for joining parted end portions of an electrical cable are well known in the art. The ends of the conductors are positioned in a tubular coupling, and the tubular coupling is crimped to secure the ends of the cable therein. The coupled cable is then provided with a moisture-resistant splice in which shrink-type tubings are positioned over the coupling at the splice, and heat is applied thereto to shrink the tubings as an outer jacket on the splice. Insulation may then be applied between the tubing and the metallic coupling.
The compression-type couplings frequently provide a greater tensile strength at the splice than the tensile strength of the conductor. Consequently, cable failure results at locations in the cable remote from the splice. Further, the compression-type couplings utilized in cable splices have a length which limits the travel of the splices over a pulley and the winding of the cable on a cable reel. This results in abrasion of the metallic conductor by the sharp end portions of the tube which restrain the spliced conductor from flexing. In addition, many tubular compression-type couplings have sharp peripheral edges that abrade or sever the insulation surrounding the cable splice upon flexing.
An example of a compression-type coupling is disclosed in U.S. Pat. No. 2,276,571 having a splice for joining together ends of electrical wires where the ends are inserted in a metal tube or sleeve that has flared end portions. After inserting the wire ends in the metal sleeve, the wires are twisted in opposite directions to effect intermingling of the strands of one wire with those of the other wire. The middle portion of the metal sleeve is then flattened by means of pliers whereby the sleeve and wires therein are compressed together to form a splice. Compressing the sleeve in this manner does not limit the degree of flattening imparted to the malleable tube so that the tensile strength in the splice is less than the tensile strength of the cable being spliced.
Intermingling of the strands of one wire with those of the other can allow stretching of the splice when the cable splice is under tension. Interweaving of the cable strands in this manner exerts a pull on only part of the copper strands initially and creates a stretching during use which ultimately destroys the insulating and water-tight seal on the splice. Further, the elongated tube when flattened provides an inflexible splice that could not be wound about a pulley or a cable reel without the sharp end portions of the tube cutting into and severing the insulation and the strands of wire at the entry and exit of the wire at the ends of the tube. Tests have revealed that substantially all of the cable splice failures are attributed to the cutting off of the conductor strands by the sharp peripheral edges of the metallic sleeve on flexing of the cable.
Cable splices and connectors that frictionally engage the conductors and include flared end portions are illustrated in U.S. Pat. Nos. 3,120,023 and 3,612,748. The former discloses an end cap in which a plurality of cable end portions are positioned in a metallic cable member having a single flared end portion. The latter is directed to an explosive connector that positions a plurality of cable end portions within a cup-shaped connector that has an inner deformable shell and an outer rigid shell with an explosive positioned therebetween. The explosive is detonated to distort the inner shell to engage the cable end portions. However, connectors of this type have sharp edge portions that are urged into contact with the cable upon flexing thereby abrading the cable ultimately, resulting in cable failure. Furthermore, the elongated configuration of the connectors in relationship to the diameter substantially reduces the flexibility of the spliced cable causing abrasion of the cable by the inner edge of the connector as the cable passes around a pulley or cable reel.
U.S. Pat. Nos. 2,314,884 and 2,467,913 disclose splices for electrical conductors in which the parted end portions of the cables are either positioned in abutting relationship or in overlapping relationship with a metallic tube. A plurality of crimped indentations are formed on the periphery of the metal tube to thereby secure the cable end portions within the metallic tube. U.S. Pat. Nos. 3,258,522 and 3,387,364 disclose encapsulating a spliced electrical conductor with a rubber-like material such as vulcanized silicone rubber to insulate the conductor splice and protect the splice from the adverse effects of moisture, abrasion and the like.
There is need for a method of joining the broken end portions of a conducting cable by a metallic sleeve that preserves the cable splice adjacent the end portions of the sleeve by reducing abrasion by the sleeve as the spliced cable passes around a pulley or is wound on a cable reel and has a tensile strength up to but not in excess of the maximum safe tensile strength of the cable being spliced.